1. Technical Field
The invention relates to a member having a separated structure composed of two regions having different compositions with each other, and a method for producing the same. The member as used in the present invention includes a plate, rod, wire, pipe and powder.
2. Description of Background Art
High level and versatile properties are required for metallic materials in accordance with expanded use of the material in a severe environment. In some cases, each part of a material is required to have different property. For complying with such requirements, a surface treatment has been applied to the material, or a clad material or a material having a sandwich structure has been devised on order to meet such requirements. However, since these methods require a complicated process and sophisticated control techniques, it was a problem that the production cost increases.
A functionally gradient material has been also devised in recent years, wherein chemical compositions and structure are changed continuously or stepwise from the inside of the material to the surface thereof. Recently, it has been studied that the material is made to have a gradient of the composition and structure by gradually changing the ratio between a metal and ceramic by using, for example, a centrifugal force, plasma sintering or plasma spraying in order to produce a material comprising a surface layer having a high hardness as well as having highly wear resistant and heat resistant, and an inner layer having high toughness (for example, Bulletin of The Iron and Steel Institute of Japan, Vol. 6 (2001), No. 1, p9˜13). The application field of such functionally gradient material is quite wide, and various properties are expected for such materials.
An example of the functionally gradient material is a Cu core solder ball. Electronic appliances are required to be small size, lightweight and highly functional while having a high processing speed. A semiconductor package being small size and capable of being mounted in high density is required for complying with such requirements as described above. A BGA (Ball Grid Array) package has been particularly noticed as a plastic based package that is able to comply with multi-pin arrangement and easy packaging.
Solder balls as being spherical powder bodies are usually used for input-output terminals of the BGA package. Sn-37Pb eutectic solder balls and Sn-36Pb-2Ag solder balls containing a small amount of silver have been frequently used for the solder balls. However, hard-core balls that are able to precisely adjust the space between the BGA package and a printed circuit board have been urgently desired in recent years, and the copper core solder balls comprising copper cores on the surface of which the Sn-37Pb eutectic solder is plated have been developed. The copper core solder ball has good heat conductivity to permit the heat generated at semiconductor devices to be promptly transferred to the printed circuit board while being excellent in electrical conductivity.